This invention relates to a printing apparatus and an ink-discharge status detection method, and more particularly, to a printing apparatus having a printhead, including a plurality of nozzles, to perform printing in accordance with an ink-jet method, and an ink-discharge status detection method used in the printing apparatus.
A printer which performs printing in accordance with the ink-jet method has a plurality of fine nozzles integrated in a high density. The printer directly discharges ink from the nozzles onto a print medium, thus forms an image by the ink dots. If impurities(dust) enter a nozzle, the ink adheres to a portion around the ink discharge orifice, or the nozzle is clogged with the impurities or the adhered ink, ink discharge failure may occur. Further, in a method of heating ink to cause film boiling and discharge the ink by the pressure of bubbles produced in a nozzle (so-called bubble-jet method), ink discharge failure may occur if disconnection occurs in a heater of the nozzle.
The ink discharge failure considerably degrades the quality of a printed image. Especially, in a production-material manufacturing apparatus such as an apparatus used for textile printing which requires very high image quality, the discharge failure is a serious problem which might lower the reliability of the apparatus.
Conventionally, a several methods have been proposed as follows to detect the discharge failure status.
(1) A print medium for detecting ink-discharge status is provided outside of an effective printing area by a printhead. Then, a pattern enabling discrimination of a nozzle in discharge failure status is printed on the print medium. Next, the pattern is optically read by using an optical reader such as a CCD camera, and a nozzle in the discharge failure status, if exists, is determined. In this case, the optical reader can be moved to the position of the print medium, otherwise, a disk or roller-shaped print medium may be used such that the print medium can be rotated to the position of the optical reader.(2) A light emitting device is provided such that a light beam emitted from the device passes through an area outside of an effective printing area by a printhead. Then, a printhead is stopped around the light axis of the light beam, and ink is discharged to block the light beam. The light beam is received by a photoreception device provided at a position opposite to the light emitting device, and it is determined whether or not discharge failure has occurred based on output from the photoreception device. According to this method, in use of a color printhead having a plurality of nozzle arrays corresponding to a plurality of color ink, the detection must be performed for the number of the nozzle arrays (the number of ink colors).
However, in the above conventional techniques, the print medium for detection or the optical reader must be moved for the discharge failure detection, or the printhead must be moved in a complicated manner different from that in normal print operation for the discharge failure detection. Accordingly, the apparatus must comprise a complicated mechanism, and further, the total printing speed of the apparatus is reduced.